VIVUS (Nasdaq: VVUS) and Arena (Nasdaq: ARNA) are higher on the session Thursday, but could part of it be due to a distant rival?

Venerable fat-fighter Weight Watchers Int'l (NYSE: WTW) is lower on the session following its second-quarter earnings report, which was released after the market closed Wednesday night. Earnings came in-line at $1.36 per share while revenue was slightly lighter than expectations.

However, Weight Watchers also cut full-year 2012 earnings expectations from a range of $4.60 to $4.80 down to $4.00 to $4.20, a 12.5 percent to just over 13 percent reduction. Does that mean more folks will turn to popping a weight-loss pill over traditional exercise and proper diet?

Weight Watchers' CEO David Kirchhoff doesn't think so. He commented on the call that Arena Pharma's (Nasdaq: ARNA) Belviq and VIVUS' (Nasdaq: VVUS) Qsymia each have their own benefits, but he's not so bullish on the potential market.

Kirchhoff notes primarily that few health plans would provide reimbursement for the pills. Then, he cites FDA language upon the approvals, saying, "I think it’s interesting to look at the FDA language around it, in which they suggested that these diet pills could be beneficial to lifestyle change efforts. To me that’s interesting because it’s not that they’re saying, “Take this pill to lose weight, and you’ll be more effective if you also change behavior.” They’re saying, “Change behavior, and this pill might make you more effective in doing so.""

He also noted that this wasn't the first threat to Weight Watchers; the company was scared when Glaxo (NYSE: GSK) and Roche's (OTCBB: RHHBY) Xenical/Alli came to market.

His solution? Full on lifestyle change, which will always win out over a pill. So, while VIVUS, Arena, and Orexigen (Nasdaq: OREX) are higher today, Weight Watchers isn't giving the potential rivals a second glance.